1. Field of the Invention
This invention relates to ignition systems for internal combustion engines, and more particularly to a method and apparatus for providing controllable, continuous energy discharges to an ignition device by oscillatory discharging and/or recharging of a capacitor through an ignition coil primary.
2. Description of the Prior Art
Conventional ignition systems have a battery, an ignition coil, a condenser (capacitor), breaker points and a distributor. These systems are known to have a number of disadvantages related to durability and performance. For example, in a typical ignition system, the voltage available to make a spark is at a maximum at idling speeds and decreases as engine speed (or ignition frequency) increases. It would be preferred to have a higher voltage available for the spark at higher firing frequencies.
With advances in solid state electronics, transistorized electronic ignition systems have become available, and automobile manufacturers now typically provide either inductive or capacitive discharge ignition systems with their products. An inductive discharge ignition system uses a transistor to cut off the current flowing in the primary winding of the ignition coil. A capacitive discharge ignition system typically uses a silicon controlled rectifier to discharge a previously charged capacitor through the primary winding of the ignition coil. As in the conventional ignition system, the voltage applied to the spark plug in an electronic ignition system typically decreases as engine speed increases.
Because the duration of the spark in the above-described ignition systems is typically relatively short (between 50 and 150 microseconds), the amount of energy that the spark plug delivers within the cylinder is limited. Moreover, if the air-to-fuel ratio is not ideal for combustion during this extremely short period of spark duration, combustion will either not occur or will be only partially complete. Spark plugs therefore become fouled, misfire and require frequent cleaning or replacement.
Recently, there has been some development toward the use of a high energy plasma to ignite fuel mixtures, and toward the use of multiple sparks and extended ignition systems. The plasma ignition systems, however, appear to have higher cost, more limited durability and higher energy requirements compared to other types of ignition systems, and they typically require a specially produced, extremely short-lived plasma plug. These systems also do not appear to provide ignition energy of long enough duration in each cylinder to ensure that substantially all combustible components of the fuel are ignited and fully burned.